1. Field of the Invention
This invention relates generally to manufacturing equipment, and more particularly to inert environment enclosures. Even more particularly, the invention relates to a feature for improving the performance of inert environment enclosures.
2. Description of the Background Art
In the electronics manufacturing industry, large-scale soldering processes and devices are currently being used to solder electrical components onto production objects such as, for example, printed circuit boards (PCB's). Typically, PCB's include multiple plated through-holes (PTHs), which receive the leads of electrical components that are to be soldered. Electrical components are typically mounted on the top surface of the PCB such that the leads pass through the PTHs and are exposed from the bottom surface of the PCB.
One process, commonly known in the art as “wave soldering”, enables several electrical joints to be soldered in a short period of time. Wave soldering typically involves passing multiple production boards through a wave soldering machine by way of a conveyor system. Production boards are either loaded directly onto the conveyor system, or multiple production boards are arranged onto a pallet that is loaded onto the conveyor system. As production boards move along the conveyor, they undergo a sequence of processes. For example, after entering the machine, the production board passes over a fluxer which applies a layer of flux onto it's bottom surface. Then, the production board passes over a heater where it is preheated to prevent thermal shock caused by sudden exposure to molten solder. After being preheated, the entire bottom surface of the production board passes over a wave of molten solder, which is projected upward via a solder nozzle. The molten solder contacts the entire bottom surface, then forms joints on any areas not covered by soldermask. The solder nozzle is supplied by a solder reservoir, which also catches any of the molten solder that does not stick. Any solder that returns to the reservoir mixes with the other molten solder and is eventually re-projected from the nozzle.
Although conventional wave soldering machines can solder several joints relatively quickly, there are drawbacks. For example, oxygen in the air reacts with the solder to form oxides (e.g., tin-oxide, lead-oxide, etc.) which accumulate on the solder nozzle and other machine components. The oxides block solder flow and, therefore, must be removed to achieve acceptable soldering. Of course, the removal of the oxides requires preventative maintenance (PM) and, therefore, equipment and manufacturing downtime. In addition, oxide formation consumes valuable solder that must be continuously replaced with new solder. As yet another drawback, oxides create environmentally hazardous materials (i.e. lead oxide).
In effort to decrease the problems caused by oxide formation, equipment manufacturers have designed wave soldering machines that operate within inert environment enclosures such as, for example, nitrogen hoods. A nitrogen hood is basically a large nitrogen filled enclosure constructed around a machine to prevent air from contacting its components. A typical nitrogen hood includes an inlet for receiving unsoldered production boards, and an outlet where finished products exit.
Although conventional nitrogen hoods help reduce the amount of oxygen within a workspace, problems still exist. For example, air can enter into conventional hoods through both the inlet and the outlet.
In an effort to decrease the problems associated with conventional nitrogen hoods, equipment manufacturers have designed nitrogen hoods with inlet and outlet curtains. Such curtains are mounted over the inlet and outlet openings to reduce air flow through the openings while also allowing production boards to move therethrough. When production boards are not being moved into or out of such hoods, the curtains hang downward to prevent air from entering. As conveyors guide production boards through the inlet or outlet, the curtains brush the top surface of the production boards to form a light “seal” between the top of the opening and the top of the production object.
Although such curtains help prevent air from entering when production boards are not being moved into or out of the hood, air still enters the hood when the machine is in use. As production objects pass into, or out of, the hood, the curtains are lifted thereby permitting the flow of air under the bottom-side of the production object.
What is needed, therefore, is an inert environment enclosure that reduces the amount of air and/or any other potentially unwanted gases that enter the enclosure when production objects are passed therethrough.